To evaluate the role of emotional regulation in depression researchers monitored the brain responses of healthy or depressed individuals to a series of images designed to provoke strong negative emotional responses - images such as car accidents and threatening-looking animals. Participants were asked to consciously work to decrease their emotional responses to some of the negative images, using techniques such as envisioning a more positive outcome than the one implied.

In both healthy and depressed individuals, they found that such efforts increased brain activity in prefrontal cortical areas known to help regulate the emotional centres of the brain, as they expected. The big difference was seen in the reactions of the emotional centres themselves, including a small almond-shaped structure called the amygdala located deep in the brain.

In nondepressed individuals, high levels of regulatory activity correlated with low activity in the emotional response centres - in effect, the healthy subjects' efforts successfully quelled their emotional responses. In depressed patients, however, high levels of activity in the amygdala and other emotional centres persisted despite intense activity in the regulatory regions.

This finding suggests that healthy people are able to effectively regulate their negative emotions through conscious effort, but that the necessary neural circuits are dysfunctional in many patients with depression, the researchers say. The difference becomes even more pronounced the harder the patients try.

"Those healthy individuals putting more cognitive effort into it are getting a bigger payoff in terms of decreasing activation in these emotional centres," lead study author Tom Johnstone from the University of Wisconsin-Madison explains. "In the depressed individuals, you find the exact opposite relationship - it seems the more effort they put in, the more activation there is in the amygdala."